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United States Patent |
5,761,983
|
Gotoh
,   et al.
|
June 9, 1998
|
Output shaft of booster
Abstract
An improvement of an output shaft of a booster is disclosed. An output
shaft 23 is formed by a push rod 24 and an adjusting screw 25. The push
rod 24 is formed with an axial bore 26 in its distal end, the axial bore
including a portion 26b of a reduced diameter which is less than an outer
diameter of a threaded section 25C of the adjusting screw. The threaded
portion is formed as a self-tapping screw. The adjusting screw includes a
guide 25D at a location which is initially inserted into the axial bore
before the threaded portion is inserted into the threaded portion. The
guide comprises a plurality of annular projections 27 having an outer
diameter which is substantially equal to the inner diameter of the axial
bore. With this construction, when the guide 25D is fitted into the
portion 26b of the axial bore 26 which has a reduced diameter, the axis of
the adjusting screw 25 may be brought into alignment with the axis of the
push rode 24. Under this condition, the threaded section 25C may be
threadably engaged with the inner periphery surface of the axial bore,
thus preventing a misalignment of the adjusting screw.
Inventors:
|
Gotoh; Hiroya (Saitama-Ken, JP);
Sugiyama; Ichirou (Saitama-Ken, JP)
|
Assignee:
|
Jidosha Kiki Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
691213 |
Filed:
|
August 1, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
92/13.2; 91/369.1; 91/376R; 92/13.8; 411/386 |
Intern'l Class: |
F01B 019/00 |
Field of Search: |
92/13.2,13.8
91/369.1,376 R
411/386,412,413,427,429
|
References Cited
U.S. Patent Documents
3527136 | Sep., 1970 | Wilson | 10/152.
|
3628422 | Dec., 1971 | Acre.
| |
3683437 | Aug., 1972 | Larson | 10/10.
|
4673323 | Jun., 1987 | Russo | 411/387.
|
4750851 | Jun., 1988 | Thomey | 411/386.
|
4818165 | Apr., 1989 | Shirai | 411/178.
|
5000639 | Mar., 1991 | Hinkley et al. | 411/386.
|
5046398 | Sep., 1991 | Hamamiya et al.
| |
5385439 | Jan., 1995 | Hurdle | 411/386.
|
Foreign Patent Documents |
59-20410 | May., 1984 | JP.
| |
Primary Examiner: Denion; Thomas E.
Attorney, Agent or Firm: Flynn, Thiel, Boutell & Tanis, P.C.
Claims
What is claimed is:
1. An output shaft of a booster including a push rod having an axial bore
formed in its distal end and an adjusting screw having a threaded portion
which is threadably enraged with the axial bore;
the improvement comprising the inner periphery surface of the axial bore
being smoothly formed to a diameter which is less than an outer diameter
of the threaded portion, and the threaded portion being formed as a
self-tapping screw, the adjusting screw having a guide at a location which
is initially inserted into the axial bore before the threaded portion is
inserted into the axial bore, the guide including a plurality of annular
projections each having an outer diameter which is substantially equal to
an inner diameter of the axial bore, the threaded portion being threadably
engaged with the inner periphery surface of the axial bore while the guide
is maintained in fitting engagement with the axial bore, and the plurality
of annular projections being each separate from an adjacent annular
projection of the plurality of annular projections.
2. An output shaft according to claim 1, in which the guide includes a
portion of a reduced diameter than the annular projections and disposed
between the plurality of annular projections and the threaded portion.
3. An output shaft according to claim 1 in which the self-tapping screw is
non-circular in cross section.
4. An output shaft according to claim 1 wherein an entrance of the axial
bore includes an increased diameter portion which is slightly greater than
an outer diameter of the threaded portion.
5. An output shaft according to claim 1 wherein an entrance of the axial
bore forms, a chamfered portion including by a tapered surface having an
increasing diameter to the outside.
6. An output shaft according to claim 4 in which the increased diameter
portion of the axial bore has a length which is sufficient to contain two
or three threads of the threaded portion.
7. An output shaft according to claim 1 in which the threaded portion is
formed with notches which are circumferentially spaced apart and which are
aligned with each other in the axial direction, whereby the self-tapping
screw is non-circular in cross section.
8. An output shaft including a push rod having an axial bore formed in its
distal end, and an adjusting screw having a threaded portion which is
threadably engaged with the axial bore;
the improvement comprising the inner periphery surface of the axial bore
being smoothly formed to a diameter which is less than an outer diameter
of the threaded portion, and the threaded portion being formed as a
self-tapping screw, the adjusting screw having a guide at a location which
is initially inserted into the axial bore before the threaded portion is
inserted into the axial bore, the guide including a plurality of annular
projections each having an outer diameter which is substantially equal to
an inner diameter of the axial bore, the threaded portion being threadably
engaged with the inner periphery surface of the axial bore while the guide
is maintained in fitting engagement with the axial bore, and the plurality
of annular projections each extending radially outwardly at about a zero
degree pitch angle.
9. An output shaft including a push rod having an-axial bore formed in its
distal end, and an adjusting screw having a threaded portion which is
threadably engaged with the axial bore;
the improvement comprising the inner periphery surface of the axial bore
being smoothly formed to a diameter which is less than an outer diameter
of the threaded portion, and the threaded portion being formed as a
self-tapping screw, the adjusting screw having a guide at a location which
is initially inserted into the axial bore before the threaded portion is
inserted into the axial bore, the guide including a plurality of annular
projections each having an outer diameter which is substantially equal to
an inner diameter of the axial bore, the threaded portion being threadably
engaged with the inner periphery surface of the axial bore while is the
guide is maintained in fitting engagement with the axial bore, and
adjacent annular projections being noncontinuous with each other.
10. An output shaft including a push rod having an axial bore formed in its
distal end, and an adjusting screw having a threaded portion which is
threadably engaged with the axial bore;
the improvement comprising the periphery surface of the axial bore being
smoothly formed to a diameter which is less than an outer diameter of the,
threaded portion, and the threaded portion being formed as a self-tapping
screw, the adjusting screw having a guide at a location which is initially
inserted into the axial bore before the threaded portion is inserted into
the axial bore, the guide including a plurality of annular projections
each having an outer diameter which is substantially equal to an inner
diameter of the axial bore, the threaded portion being threadably engaged,
with the inner periphery surface of the axial bore while the guide is
maintained in fitting engagement with the axial bore, adjacent annular
projections being noncontinuous with each other, and each of said
plurality of annular projections extending outwardly from said guide
portion at about a zero degree pitch angle.
Description
FIELD OF THE INVENTION
The invention relates to an output shaft of a booster, and more
particularly, to an output shaft comprising a push rod and an adjusting
screw which is threadably engaged therewith.
DESCRIPTION OF THE PRIOR ART
Generally an output shaft of a booster comprises a push rod having an axial
bore formed in its distal end, and an adjusting screw having threads which
are threadably engaged with the axial bore. By adjusting the amount of the
threadable engagement between the adjusting screw and the push rod, the
axial length of the overall output shaft can be adjusted.
To secure the adjusting screw while it is threadably engaged with the push
rod, it has been the prior art practice to form female threads in the
axial bore of the push rod while forming a male thread comprising an
incomplete thread on the adjusting screw, which is then threadably engaged
with the female threads to secure the both integrally together.
In the described arrangement, the need to form female threads in the axial
bore of the push rod and to form a male thread on the adjusting screw
which comprises an incomplete thread resulted in an increased cost.
To overcome such drawback, it is contemplated to form a thread on the
adjusting screw by a self-tapping screw while the inner peripheral surface
of the axial bore be formed smoothly to a diameter which is less than the
outer diameter of the thread on the adjusting screw so that the
self-tapping screw may be threadably engaged with the inner periphery
surface of the axial bore. This makes it possible to manufacture the
output shaft inexpensively. On the other hand, this involves a risk that
the self-tapping screw may be skewed when it is threadably engaged with
the axial bore. In such event, the output shaft may drive a piston of a
master cylinder along an oblique line of action, resulting in a risk that
a smooth braking operation may be impeded.
SUMMARY OF THE INVENTION
In view of the foregoing, the invention provides an output shaft of a
booster which enables a reliable threadable engagement between a push rod
and an adjusting screw on an aligned axis and which can be manufactured
inexpensively.
Specifically, in accordance with the invention, an improvement is applied
to an output shaft of a conventional booster in that the inner periphery
surface of the axial bore is smoothly formed to a diameter less than the
outer diameter of the threads, which are formed as a self-tapping screw.
The tapping screw is provided with a guide at a location which is
initially inserted into the axial bore before the threads are inserted
into the axial bore, the guide comprising a plurality of annular
projections having an outer diameter which is substantially equal to the
inner diameter of the axial bore, the threads being threadably engaged
with the inner periphery surface of the axial bore while the guide is
maintained in fitting engagement with the axial bore.
With the construction according to the invention, the guide formed at a
distal end of the adjusting screw has an outer diameter which is
substantially equal to the inner diameter of the axial bore in the push
rod, and accordingly, the axis of the adjusting screw can be brought into
alignment with the axis of the push rod by the presence of the guide.
While such alignment is maintained, the self-tapping screw can be
threadably engaged with the inner periphery surface of the axial bore in
the push rod. The plurality of annular projections which form the guide
can be utilized in achieving a balance of forces when rolling the
adjusting screw, thus allowing the accuracy of rolling the self-tapping
screw to be improved.
The above and other objects, features and advantages of the invention will
become apparent from the following description of an embodiment thereof
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of one embodiment of the invention;
FIG. 2 is an enlarged cross section of part thereof;
FIG. 3 is a right-hand side elevation of an adjusting screw 25 shown in
FIG. 2;
FIG. 4 is a fragmentary cross section of a push rod 24 before an adjusting
screw 25 is threadably engaged therewith; and
FIG. 5 is a view similar to FIG. 4 but showing the axial bore having a
chamfered region.
DETAILED DESCRIPTION OF THE EMBODIMENT
An embodiment of the invention will now be described with reference to the
drawings. FIG. 1 shows a general arrangement of a brake booster of single
type including an enclosed vessel, formed by a front shell 1 and a rear
shell 2, in which an substantially tubular valve body 3 is slidably
disposed. A power piston 4 is attached around the outer periphery of the
valve body 3, and a diaphragm 5 is applied to the back surface of the
power piston, thereby dividing the interior of the enclosed vessel into a
forwardly located constant pressure chamber 6 and a rearwardly located
variable pressure chamber 7.
The valve body 3 contains a valve mechanism 8 which switches a fluid
circuit. Specifically, the valve mechanism 8 comprises an annular, first
valve seat 10 formed around the inner periphery of the valve body 3, an
annular, second valve seat 12 formed on the right end of a valve plunger
11 which is slidably fitted into the valve body 3, and a valve element 14
which is adapted to be seated upon either valve seat 10 or 12 from the
right, as viewed in FIG. 1, under the influence of a spring 13.
A space located radially outward of the first valve seat 10 communicates
with the constant pressure chamber 6 through an axial constant pressure
passage 15 formed in the valve body 3, and the constant pressure chamber 6
in turn communicates with an intake manifold of an engine through a tubing
16 which is mounted on the front shell 1 for introducing a negative
pressure. In this manner, a negative pressure is normally introduced into
the constant pressure chamber 6. A space located intermediate the first
valve seat 10 and the second valve seat 12 communicates with the variable
pressure chamber 7 through a radial valve pressure passage 17 formed in
the valve body 3. A space located radially inward of the second valve seat
12 communicates with the atmosphere through a pressure passage 18 formed
in the valve body 3.
The right end of the valve plunger 11 is pivotally connected to the distal
end of an input shaft 20, the terminal end of which is coupled to a brake
pedal, not shown. A plate plunger 21 and a reaction disk 22 are
sequentially disposed to the left of the valve plunger 18, and the
reaction disk 22 is received in a recess formed in one end of an-output
shaft 23 which is slidably disposed in the valve body 3.
The output shaft 23 comprises a push rod 24, and an adjusting screw 25
which is integrally and threadably engaged with the distal end of the push
rod 24. The distal end of the output shaft 23 which projects externally of
the front shell 1 is connected to a piston of a master cylinder, not
shown, which is connected to the front shell 1.
FIG. 2 is an enlarged cross section of an inventive part of the output
shaft 23. The adjusting screw 25, which forms the output shaft 23,
comprises a cylindrical body 25A, a hexagonal section 25B which is
utilized to rotate the adjusting screw 25, a threaded section 25C which is
adapted to be threadably engaged with the push rod 24, and a guide 25D
which serves maintaining the threaded section 25C in axial alignment with
the push rod 24 when the screw and push rod are threadably engaged
together. The left end face of the body 25A is disposed in abutment
against the piston of a master cylinder, not shown.
The push rod 24, which also forms the output shaft 23, has a distal end
(left end in FIGS. 1, 2, 4, 5) in which an axial bore 26 is formed, into
which the threaded section of 25C of the adjusting screw 25 is to be
threadably engaged. FIG. 4 shows the status of the axial bore 26 before
the threaded section 25C is threadably engaged therewith. As shown, the
axial bore includes a portion 26a of an increased diameter or an inner
diameter d1 which is slightly greater than the outer diameter of the
threaded section 25C and which is disposed at the entrance to the axial
bore, and another portion 26b of a reduced diameter or an inner diameter
d2 which is less than the outer diameter of the threaded section 25C and
which continues from the portion 26a. The portion 26a of an increased
diameter has an axial length L which is chosen to be capable of receiving
two or three threads of the threaded section 25C.
Referring to FIGS. 2 and 3, the threaded section 25C of the adjusting screw
25 is formed as a self-tapping screw having a generally slight conical
taper along its right-hand end, or the end which is initially inserted
into the axial bore 26 in the push rod 24. In a region located to the
right thereof, the guide 25D is provided with a plurality of annular
projections 27 having an outer diameter which is less than the outer
diameter of the threaded section 25C and which is substantially equal to
the inner diameter of the portion 26b of the axial bore 26. In addition,
the guide 25D includes a solid cylindrical portion 28 of a reduced
diameter or a diameter less than the outer diameter of the annular
projections 27, which is located to the left of the annular projections or
in a region between the annular projections 27 and the threaded section
25C.
It is to be noted that the threaded section 25C is periphery and partly
formed with notches 30 which are disposed at three circumferentially
spaced locations in the embodiment shown and which are aligned with each
other in the axial direction. In the region of these notches 30, the
threaded section 25C is sized to avoid abutment against the inner
periphery surface of the portion 26b of the axial bore 26. The purpose of
providing the notches 30 is to reduce a friction when the threaded section
25C is threadably engaged with the portion 26b of the axial bore 26.
In the embodiment, the outer periphery of the thread section 25C is partly
formed with the notches 30, whereby it is constructed as a self-tapping
screw which is non-circular in cross section. However, it should be
understood that the construction of the self-tapping screw is not limited
thereto, but a self-tapping screw of any suitable cross section and
configuration known in the art may be similarly employed. In the present
embodiment, the annular projections 27 are also formed with corresponding
notches, but the notches 30 in the annular projections 27 may be omitted.
The purpose of the portion 28 of a reduced diameter which is disposed
between the annular projections 27 and the threaded section 25C is to
secure a full functioning of the guide by increasing the overall length of
the guide 25D while preventing an increase in the friction which results
from an increased overall length of the guide 25D.
When attaching the adjusting screw 25 with the push rod 24, the guide 25D
is initially brought into a close fit into the portion 26b of a reduced
diameter formed in the axial bore 26. Under this condition, the presence
of the guide 25D allows the axis of the adjusting screw 25 to be brought
into alignment with the axis of the push rod 24. Since each annular
projection 27 of the guide 25D formes a line contact with the inner
periphery surface of the portion 26b having a reduced diameter, the guide
25D can be fitted into the portion 26b with a reduced force.
When the thread section 25C abuts against a step between the portions 26a
and 26b of the axial bore 26 which have an increased and a reduced
diameter, respectively, the hexagonal section 25B may be utilized to turn
the adjusting screw 25 in a given direction, whereupon threads 25c bite
into the inner periphery surface of the portion 26b of a reduced diameter
for threadable engagement therewith. Subsequently, the degree of
threadable engagement of the adjusting screw 25 may be adjusted so that
the overall length of the output shaft 23 becomes equal to a proper axial
size. Since a misalignment of the adjusting screw 25 is prevented by the
guide 25D which is fitted into the portion 26b of a reduced diameter, the
adjusting screw 25 can be threadably engaged with the push rod 24 while
maintaining an alignment therebetween.
Because the guide 25D is provided with the plurality of annular projections
27 in the adjusting screw 25 as described above, these projections can be
utilized in achieving a balance of forces when rolling the adjusting screw
25, thus enabling an improvement of the accuracy of rolling the thread
section 25C.
The portion 26a of the axial bore 26 which has an increased diameter may be
omitted, and instead a chamfered region comprising a tapered surface
having an increasing diameter to the outside may be formed at the entrance
to the axial bore 26 (FIG. 5).
While the invention has been disclosed above with reference to a preferred
embodiment, it should be understood that a number of changes,
modifications and substitutions therein can be made without departing from
the spirit and scoop of the invention defined by the appended claims.
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